Time and chance: the stochastic nature of disease causation

• Published in: The Lancet (British edition) 2005-04, Vol.365 (9468), p.1434-1437
• Main Authors: Coggon, DIW, Martyn, CN
• Format: Article
• Language: English
• Subjects: Causality; Disease; Disease - etiology; Elastic properties; Health care; Health risk assessment; Humans; Intervention; Risk factors; Stochastic Processes
• ISSN: 0140-6736; 1474-547X
• DOI: 10.1016/S0140-6736(05)66380-5

Though we smile at [Samuel Pepys]' hare's foot amulet and turpentine pill, his doubts about their effectiveness might contain more truth than the aspirations of the grant applicants. Obviously, a patient with a disease must have been exposed to a combination of causes sufficient to induce that disease, but it does not necessarily follow that these causes are measurable or even identifiable. An analogy can be drawn with the throw of a die. The fact that a six is rolled does not mean that the die was heavily exposed to any risk factors for that outcome. Instead, this result is due to the operation of a complex set of circumstances (dimensions, shape, and weight of the die; the exact position of its centre of gravity; forces acting on it and its height above the ground when thrown; viscosity of the air; contour and elastic properties of the surface on which it landed, and so on), none of which could be shown to have a consistent effect on its own on whether the die rolls six-except, of course, in the trivial circumstance of dropping it very gently from minimum height with the six face up. In this essay we review the nature of disease causation, and argue that the role of stochastic processes is underappreciated. Advances in understanding of pathogenic mechanisms or genetic susceptibility might not enable us to explain why one person gets a disease and another does not.